The present invention relates to liquid crystalline media and to liquid crystal displays comprising these media, especially to displays addressed by an active matrix (AMDs) and in particular to displays addressed by thin film transistors (TFTs), especially for projection type displays. Preferably, the TFTs are prepared on silicon (LCoS). The inventive media are also well suited for displays of the optically compensated bend (OCB) mode.
Liquid Crystal Displays (LCDs) are widely used to display information. Electro-optical modes employed are, e.g., the twisted nematic (TN)-, the super twisted nematic (STN)-, the optically compensated bend (OCB)- and the electrically controlled birefringence (ECB)-mode with their various modifications, as well as others. Besides these modes, which all do use an electrical field, which is substantially perpendicular to the substrates, respectively to the liquid crystal layer, there are also electro-optical modes employing an electrical field substantially parallel to the substrates, respectively the liquid crystal layer, like, e.g., the In-Plane Switching mode (as disclosed, e.g., in DE 40 00 451 and EP 0 588 568). Especially this electrooptical mode is used for LCDs for modern desk top monitors.
The liquid crystals according to the present invention are preferably used in AM addressed displays in particular in TFTs displays, especially for projection type displays. Preferably the TFTs are prepared on silicon (LCoS). The inventive media are also well suited for displays of the OCB mode.
For these displays new liquid crystalline media with improved properties are required. Especially the birefingence (xcex94n) should be sufficiently high. Further, the dielectric anisotropy (xcex94xcex5) should be high enough to allow a reasonably low operation voltage. Preferably, xcex94xcex5 should be higher than 7 and very preferably be higher than 9, or even higher than 10, but preferably not higher than 19 and in particular not higher than 15. Otherwise, the resistivity of the mixtures tends to become inacceptably low for most TN-AMDs. Besides this parameter, the media have to exhibit a suitably wide range of the nematic phase, a rather small rotational viscosity and, as mentioned above, an at least moderately high specific resistivity.
The displays according to the present invention are preferably addressed by an active matrix (active matrix LCDs, short AMDs), preferably by a matrix of thin film transistors (TFTs). However, the inventive liquid crystals can also beneficiously be used in displays with other known addressing means.
There are various different display modes using composite systems of liquid crystal materials of low molecular weight together with polymeric materials such as, e.g., polymer dispersed liquid crystal (PDLC)-, nematic curvilinearily aligned phase (NCAP)- and polymer network (PN)-systems, as disclosed, for example, in WO 91/05 029 or axially symmetric microdomain (ASM) systems and others. In contrast to these, the modes especially preferred according to the instant invention are using the liquid crystal medium as such, oriented on surfaces. These surfaces typically are pretreated to achieve uniform alignment of the liquid crystal material. The display modes according to the instant invention preferably use an electrical field substantially perpendicular to the composite layer.
LCDs are used for direct view displays, as well as for projection type displays.
Liquid crystal compositions with a high value of the birefringence suitable for LCDs and especially for AMD displays are known, e.g., from U.S. Pat. No. 5,328,644, JP 06-264 059 (A) and DE 199 19 348. These compositions, however, do all have significant drawbacks. Most of them have, amongst other deficiencies, too low values of the birefringence and/or require operation voltages which are too high. Many of them also have too low resistivities, especially after exposure to elevated temperature and/or intense actinic radiation, in particular strong visible light and/or UV radiation. Many of the media of the prior art do further lead to unfavourably long response times.
Thus, there is a significant need for liquid crystalline media with suitable properties for practical applications such as a wide nematic phase range, low viscosities, a high xcex94xcex5, a sufficiently high resistivity and, in particular, an appropriately high optical anisotropy xcex94n, according to the display mode used.
Surprisingly, it now has been found that liquid crystalline media with a suitably high xcex94xcex5, a suitable phase range, xcex94n and a sufficiently high resistivity can be realised, which do not exhibit the drawbacks of the materials of the prior art or at least do exhibit them to a significantly lesser degree.
These improved liquid crystalline media according to the instant application comprise at least the following components:
a dielectrically positive component, component A, consisting of dielectrically positive compounds, comprising one or more compounds of formula I, one or more compounds of formula II and optionally one or more compounds, preferably selected from the group of compounds of formulae of formula III, IVa and V and optionally further dielectrically positive compounds 
wherein
R1, R2, R3, R4 and R5 independently of each other, are alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy with 1 to 7 C-atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl with 2 to 7 C-atoms,
X1, X2, X3 and X5 independently of each other, are F, Cl or fluorinated alkyl or fluorinated alkoxy, each with 1 to 4 C-atoms, preferably
X1 and X5 are, independently of each other, F or Cl, most preferably F and
X2 and X3 are, independently of each other, F or Cl, most preferably Cl,
X4 is fluorinated alkyl or fluorinated alkoxy, each with 1 to 4 C-atoms, preferably OCF3 or OCF2H,
Y51 and Y52 are, independently of each other, H or F and
n is 0, 1 or 2, preferably 1 or 2, most preferably 2,
wherein, optionally, two of the 6-membered rings in formulae I, and III to V may be linked by a group selected from
xe2x80x94CH2xe2x80x94CH2xe2x80x94, xe2x80x94CF2xe2x80x94CF2xe2x80x94, xe2x80x94CF2xe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94CF2xe2x80x94 and xe2x80x94COxe2x80x94Oxe2x80x94, preferably xe2x80x94CH2xe2x80x94CH2xe2x80x94 and xe2x80x94CF2xe2x80x94Oxe2x80x94, most preferably xe2x80x94CH2xe2x80x94CH2xe2x80x94,
a dielectrically neutral component, component B, consisting of dielectrically neutral compounds, comprising one or more compounds of formula IVb 
wherein
R4xe2x80x2 is alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy with 1 to 7 C-atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl with 2 to 7 C-atoms,
X4xe2x80x2 is F or Cl, preferably F,
wherein, optionally, two of the 6-membered rings may be linked by a group selected from
xe2x80x94CH2xe2x80x94CH2xe2x80x94, xe2x80x94CF2xe2x80x94CF2xe2x80x94, xe2x80x94CF2xe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94CF2xe2x80x94 and xe2x80x94COxe2x80x94Oxe2x80x94, preferably xe2x80x94CH2xe2x80x94CH2xe2x80x94 and xe2x80x94CF2xe2x80x94Oxe2x80x94, most preferably xe2x80x94CH2xe2x80x94CH2xe2x80x94, and
optionally, a dielectrically negative component, component C, consisting of dielectrically negative compounds.
Preferably, the dielectrically positive component, component A comprises one or more compounds each of formulae I, II IVb and one or more compounds selected from the group of compounds each of formulae III, IVa and V and in particular one or more compounds each of formulae III and V.
Further, the dielectrically positive component, component A, optionally comprises one or more compounds of formula VI 
wherein
R6 is alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy with 1 to 7 C-atoms, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl with 2 to 7 C-atoms,
X6 is F, Cl or fluorinated alkyl or fluorinated alkoxy, each with 1 to 4 C-atoms, preferably F or Cl, most preferably F,
Y6 is H or F and
m is 0, 1 or 2, preferably 1 or 2 and most preferably 1,
wherein, optionally, two of the 6-membered rings may be linked by an group selected from
xe2x80x94CH2xe2x80x94CH2xe2x80x94, xe2x80x94CF2xe2x80x94CF2xe2x80x94, xe2x80x94CF2xe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94CF2xe2x80x94 and xe2x80x94COxe2x80x94Oxe2x80x94, preferably xe2x80x94CH2xe2x80x94CH2xe2x80x94 and xe2x80x94CF2xe2x80x94Oxe2x80x94, most preferably xe2x80x94CH2xe2x80x94CH2xe2x80x94
The liqiud crystral mixtures according to the present invention comprise a dielectrically neutral component, component B. This component has a dielectrical anisotropy in the range from xe2x88x921.5 to +3. Preferably, it contains essentially, and especially preferably, entirely dielectrically positive compounds. Preferably, this component, besides one or more compounds of formula IVb, comprises one or more dielectrically neutral compounds of formula VII 
wherein
R71 and R72, independently of each other, have the meaning given for R1 under formula I above, 
independently of each other, and in case 
is present twice, also these, independently of each other, are 
preferably at least one of 
and preferably at least one of 
Z71 and Z72 are, independently of each other, and in case Z71 is present twice, also these independently of each other, xe2x80x94CH2CH2xe2x80x94, xe2x80x94COOxe2x80x94, trans-CHxe2x95x90CHxe2x80x94, trans-CFxe2x95x90CFxe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94CF2Oxe2x80x94 or a single bond, preferably at least one of them is a single bond and most preferably all are single bonds, and
k is 0, 1 or 2, preferably 1 or 2
from which the compounds of formula IVb are excluded.
Optionally, the liqiud crystral mixtures according to the present invention comprise a dilectrically negative, component C. This component has a dielectrical anisotropy below xe2x88x921.5, and consists of dielectrically negative compounds and comprises compounds of formula VIII 
wherein
R81 and R82 independently of each other have the meaning given for R1 under formula I above, 
and the other one has one of the meanings given for 
or is 
L81 and L82 are, independently of each other, xe2x95x90C(xe2x80x94F)xe2x80x94 or xe2x95x90Nxe2x80x94, preferably at least one one of them is xe2x95x90C(xe2x80x94F)xe2x80x94 and most preferably both of them are xe2x95x90C(xe2x80x94F)xe2x80x94 and
Z81 and Z82 are, independently of each other, xe2x80x94CH2CH2xe2x80x94, xe2x80x94COOxe2x80x94, trans-CHxe2x95x90CHxe2x80x94, trans-CFxe2x95x90CFxe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94CF2Oxe2x80x94 or a single bond, preferably at least one of them is a single bond and most preferably all are a single bond, and
i is 0 or 1.
Preferably, the liquid crystalline media according to the instant invention contain a component A comprising, preferably predominantly consisting of and most preferably entirely consisting of compounds selected from formulae I to VIII.
Comprising in this application means in the context of compositions that the entity referred to, e.g., the medium or the component, contains the component or components or the compound or compounds in question, preferably in a total concentration of 10% or more, and most preferably of 20% or more.
Predominantly consisting, in this context, means that the entity referred to contains 80% or more, preferably 90% or more, and most preferably 95% or more of the component or components or of the compound or compounds in question.
Entirely consisting, in this context, means that the entity referred to contains 98% or more, preferably 99% or more, and most preferably 100.0% of the component or components or of the compound or compounds in question.
Preferably, component A comprises one or more compounds of formula I, wherein X1 is F. Preferably, component A further comprises one or more compounds of formula II, wherein X2 is Cl. Also, preferably component A comprises one or more compounds of formula III, wherein X3 is Cl and/or one or more compounds of formula IVa wherein X4 is F.
The compounds of formula V are preferably selected from the group of sub-formulae V-1 to V-12
wherein
R5 and X5 have the respective meanings given under formula V above and preferably
R5 is n-alkyl with 1 to 5 C-atoms and
X5 is F, Cl, xe2x80x94CF3 or xe2x80x94OCF3, most preferably F.
Especially preferred are the media which contain compounds of formula V selected from the group of sub-formulae V-5 to V-12, most preferably V-5 to V-8 and V-12 and in particular V-5, V-7, V-8 and V-12.
The compounds of formula VI are preferably selected from the group of sub-formulae VI-1 to VI-18
wherein
R6 and X6 have the respective meanings given under formula VI above and preferably
R6 is n-alkyl with 1 to 5 C-atoms or alkenyl with 2 to 5 C-atoms and
X6 is F, Cl, xe2x80x94CF3 or xe2x80x94OCF3, preferably F or Cl and most preferably F.
Most preferably the medium contains compounds of formula VI selected from the group of sub-formulae VI-7 to VI-15 and in particular VI-8 and VI-9.
Especially preferred are further media comprising compounds selected from the group of formulae VI-8, VI-11 and VI-14 and/or VI-9, VI-12 and VI-15, in particular with R6 being alkenyl, especially vinyl.
In a preferred embodiment the liquid crystalline media according to the instant invention contains a component B comprising, preferably predominantly consisting of, and most preferably entirely consisting of compounds selected from the group of formulae IVb and VII.
In a further preferred embodiment the liquid crystal medium contains a liquid crystal component C, which is preferably predominantly consisting of, and most preferably entirely consisting of compounds of formula VIII.
This component C may be present, and preferably is present, besides components A and B.
The compounds of formula VII are preferably selected from the group of sub-formulae VII-1 to VII-10
wherein
R71 and R72 have the meaning given under Formula VII above.
Most preferably the medium contains compounds of formula VII selected from the group of sub-formulae VII-1, VII-2, VII-4, VII-6, VII-8 and VII-10, and in particular VII-4, VII-6, VII-8 and VII-10.
Especially preferred are further media comprising compounds selected from the group of formula VII-3 and in particular with R72 being alkenyl, especially vinyl.
Also other mesogenic, as well as nonmesogenic, compounds, which are not explicitly mentioned above, can optionally and beneficiously be used in the media according to the instant invention. Such compounds are known to the expert in the field.
In a preferred embodiment the medium comprises one or more compounds of formula V-5 and/or V-7, preferably with R5 being n-alkyl, preferably with 2 to 5 C-atoms.
In a further preferred embodiment, which may be identical to the one above, the medium comprises one or more compounds of formula V-8, preferably with R5 being n-alkyl, preferably with 2 to 5 C-atoms.
Preferably, the medium comprises one or more compounds of formula VI-6 preferably with R6 being n-alkyl, preferably with 3 to 5 C-atoms, or alkenyl, preferably vinyl, and with X6 being preferably Cl or F, most preferably F.
Preferably, the medium comprises one or more compounds of formula VII-4 and/or, preferably, VII-6, preferably together with one or more compounds of formula VII-8 and/or, preferably, VII-10. In these compounds of formulae VII-4, VII-6, VII-8 and VII-10 R71 and R72 are preferably, independently from each other, n-alkyl, preferably with 3 to 5 C-atoms.
Component A preferably is used in a concentration from 50% to 100%, preferably from 60% to 100%, more preferably from 70% to 100% and most preferably from 80% to 100%, preferably up to to 90% of the total mixture.
Component B preferably is used in a concentration from more than 0% to 80%, preferably from more than 0% to 30%, more preferably from 2% to 20% and most preferably from 4% to 15% of the total mixture.
Component C preferably is used in a concentration from 0% to 30%, preferably from 0% to 20% and most preferably from 0% to 10% of the total mixture.
Optionally, the inventive media can comprise further liquid crystal compounds in order to adjust the physical properties. Such compounds are known to the expert. Their concentration in the media according to the instant invention is preferably 0% to 30%, more preferably 0% to 20% and most preferably 0.5% to 15%.
Preferably, the liquid crystal medium contains 50% to 100%, more preferably 70% to 100% and most preferably 80% to 100% and in particular 90% to 100% totally of components A, B and C, which contain, preferably predominantly consist of, and most preferably entirely consist of one or more of compounds of formulae I to VIII, respectively.
The liquid crystal media according to the instant invention are characterized by a clearing point of 90xc2x0 C. or more, preferably of 95xc2x0 C. or more and in particular of 100xc2x0 C. or more.
The xcex94n of the liquid crystal media according to the instant invention is 0.170 or more, preferably in the range of 0.180 to 0.280, more preferably in the range of 0.190 to 0.250, most preferably in the range of 0.195 to 0.230 and in particular in the range of 0.200 to 0.225.
The xcex94xcex5, at 1 kHz and 20xc2x0 C., of the liquid crystal media according to the invention is 7.0 or more, preferably 9.0 or more, most preferably 10.0 or more and in particular 11.5 or more. It is, however, preferably 20.0 or less, more preferably 17.0 or less and most preferably 15.0 or less.
Preferably, the nematic phase of the inventive media extends at least from 0xc2x0 C. to 90xc2x0 C., more preferably at least from xe2x88x9220xc2x0 C. to 80xc2x0 C., more preferably at least from xe2x88x9220xc2x0 C. to 90xc2x0 C., most preferably at least from xe2x88x9230xc2x0 C. to 90xc2x0 C., and in particular at least from xe2x88x9230xc2x0 C. to 100xc2x0 C., wherein at least means that preferably the lower limit is under cut, wherein the upper limit is surpassed.
In the present application the term dielectrically positive compounds describes compounds with xcex94xcex5 greater than 3.0, dielectrically neutral compounds are compounds with xe2x88x921.5xe2x89xa6xcex94xcex5xe2x89xa63.0, and dielectrically negative compounds are compounds with xcex94xcex5 less than xe2x88x921.5. The same holds for components. xcex94xcex5 is determined at 1 kHz and 20xc2x0 C. The dielectrical anisotropies of the compounds is determined from the results of a solution of 10% of the individual compounds in a nematic host mixture. The capacities of these test mixtures are determined both in a cell with homeotropic and with homogeneous alignment. The cell gap of both types of cells is approximately 10 xcexcm. The voltage applied is a rectangular wave with a frequency of 1 kHz and a root mean square value typically of 0.5 V to 1.0 V, however, it is always selected to be below the capacitive threshold of the respective test mixture.
For dielectrically positive compounds the mixture ZLI-4792 and for dielectrically neutral, as well as for dielectrically negative compounds, the mixture ZLI-3086, both of Merck KGaA, Germany are used as host mixture, respectively. The dielectric permittivities of the compounds are determined from the change of the respective values of the host mixture upon addition of the compounds of interest and are extrapolated to a concentration of the compounds of interest of 100%. Components having a nematic phase at the measurement temperature of 20xc2x0 C. are measured as such, all others are treated like compounds.
The term threshold voltage refers in the instant application to the optical threshold and is given for 10% relative contrast (V10) and the term saturation voltage refers to the optical saturation and is given for 90% relative contrast (V90) both, if not explicitly stated otherwise. The capacitive threshold voltage (V0, also called Freedericksz-threshold VFr) is only used if explicitly mentioned.
The ranges of parameters given in this application are all including the limiting values, unless explicitly stated otherwise.
Throughout this application, unless explicitly stated otherwise, all concentrations are given in mass percent and relate to the respective complete mixture, all temperatures are given in degrees centigrade (Celsius) and all differences of temperatures in degrees centigrade. All physical properties have been and are determined according to xe2x80x9cMerck Liquid Crystals, Physical Properties of Liquid Crystalsxe2x80x9d, Status November 1997, Merck KGaA, Germany and are given for a temperature of 20xc2x0 C., unless explicitly stated otherwise. The optical anisotropy (xcex94n) is determined at a wavelength of 589.3 nm. The dielectric anisotropy (xcex94xcex5) is determined at a frequency of 1 kHz. The threshold voltages, as well as all other electro-optical properties have been determined with test cells prepared at Merck KGaA, Germany. The test cells for the determination of xcex94xcex5 had a cell gap of 22 xcexcm. The electrode was a circular ITO electrode with an area of 1.13 cm2 and a guard ring. The orientation layers were lecithin for homeotropic orientation (xcex5∥) and polyimide AL-1054 from Japan Synthetic Rubber for homogeneuous orientation (xcex5xe2x8axa5). The capacities were determined with a frequency response analyser Solatron 1260 using a sine wave with a voltage of 0.3 Vrms. The light used in the electro-optical measurements was white light. The set up used was a commercially available equipment of Otsuka, Japan. The characteristic voltages have been determined under perpendicular observation. The threshold (V10)-mid grey (V50)- and saturation (V90) voltages have been determined for 10%, 50% and 90% relative contrast, respectively.
The liquid crystal media according to the present invention can contain further additives and chiral dopants in usual concentrations. The total concentration of these further constituents is in the range of 0% to 10%, preferably 0.1% to 6%, based on the total mixture. The concentrations of the individual compounds used each are preferably in the range of 0.1% to 3%. The concentration of these and of similar additives is not taken into consideration for the values and ranges of the concentrations of the liquid crystal components and compounds of the liquid crystal media in this application.
The inventive liquid crystal media according to the present invention consist of several compounds, preferably of 3 to 30, more preferably of 8 to 20 and most preferably of 10 to 16 compounds.
These compounds are mixed in conventional way. As a rule, the required amount of the compound used in the smaller amount is dissolved in the compound used in the greater amount. In case the temperature is above the clearing point of the compound used in the higher concentration, it is particularly easy to observe completion of the process of dissolution. It is, however, also possible to prepare the media by other conventional ways, e.g. using so called pre-mixtures, which can be e.g. homologous or eutectic mixtures of compounds or using so called multi-bottle-systems, the constituents of which are ready to use mixtures themselves.
By addition of suitable additives, the liquid crystal media according to the instant invention can be modified in such a way, that they are usable in all known types of liquid crystal displays, either using the liquid crystal media as such, like TN-, TN-AMD, ECB-AMD, VAN-AMD, IPS and OCB LCDs and in particular in composite systems, like PDLC, NCAP, PN LCDs and especially in projectoin type TFT displays.
The melting point T(C,N), the transition from the smectic (S) to the nematic (N) phase T(S,N) and the clearing point T (N,I) of the liquid crystals are given in degrees centigrade.
In the present application and especially in the following examples, the structures of the liquid crystal compounds are represented by abbreviations also called acronyms. The transformation of the abbreviations into the corresponding structures is straight forward according to the following two tables A and B. All groups CnH2n+1 and CmH2m+1 are straight chain alkyl groups with n respectively m C-atoms. The interpretation of table B is self evident. Table A does only list the abbreviations for the cores of the structures. The individual compounds are denoted by the abbreviation of the core followed by a hyphen and a code specifying the substituents R1, R2, L1 and L2 follows:
The entire disclosure of all applications, patents and publications, cited herein and of corresponding European application No. 01125182.4, filed Oct. 23, 2001, is incorporated by reference herein.
The liquid crystal media according to the instant invention do contain preferably
seven or more, preferably eight or more compounds, preferably of different formulae, selected from the group of compounds of formulae of tables A and B and/or
one, two or more, preferably three or more compounds, preferably of different formulae, selected from the group of compounds of formulae of table A and/or
two, three, four or more, preferably five or more compounds, preferably of different formulae, selected from the group of compounds of formulae of table B.